Staring
burner control system



March 23, 19 B. J. STARING 3,174,523

' BURNER CONTROL SYSTEM Filed July 16, 1962 2 Sheets-Sheet 1 1/50 '-1 E 95 L 7; k 29 Q I I J 0/ [/7 V5- h 702 fife/#12005 J 5 Mel/16' 5/ MM/Ad United States Patent C) 3,174,528 EURNER CUNTROL SYSTEM Bernardus J. Staring, Markham, Ontario, Canada, assignor to White-Rodgers Company, St. Louis, Mo., a corporation of Missouri Filed July 16, 1962, Ser. No. 210,079 13 Claims. (Cl. 158-28) This invention relates to automatic control systems for fluid fuel burner which include safety means operative to permit the continued supply of fuel to the burner when there is combustion and to cut off the flow of fuel if combustion fails to occur within a predetermined interval during which fuel is supplied or if combustion having been established subsequently fails.

An object of the invention is to provide a generally new and improved safety control system for fluid fuel burners which is instantly responsive to the appearance or disappearance of combustion flame and which is particularly economical in construction and reliable in operation.

A further object is to provide a burner control system in which a thermal time switch including an electrical resistance heater determines the trial period during which fuel is supplied to the burner in the absence of combustion and in which an instantly responsive combustion flame detection circuit is employed which is capable of passing suflicient current in the presence of flame to render the electrical resistance heater inoperative by direct shunting without the necessity of employing relay means.

A further object is to provide a burner control system in which an instantly responsive flame detection network becomes conductive in the presence of the light of combustion flame and thereby permits the continued flow of fuel to the burner once such flow is initiated and in which initiation of any flow of fuel to the burner is prevented in event the flame detection network is for any reason defectively conductive.

Further objects and advantages will appear from the following description when read in connection with the accompanying drawings.

FIG. 1 of the drawings is a diagrammatic illustration of a control system for a conventional, pressure-type, oil burner embodying a first form of the invention in which the burner ignition means is constantly operative during burner operation; and

FIG. 2 is a diagrammatic illustration of a second form of the present invention in which operation of the burner ignition means is cut off after successful ignition is established.

Referring to FIG. 1 of the drawings, the primary elements of the system are: an oil burner having a driving motor 12, a space thermostat 14, a motor relay having a winding 16, normally closed contacts 18, and normally.

open contacts 20, 22, and 24, a thermal time switch (safety switch) having normally closed contacts 26 and a resistance heater 28, a thermal time switch (scavenging switch) having normally closed contacts 30 and a resistance heater 32, a light sensitive element 34, a silicon controlled rectifier 36 having a control network consisting of a resistor 40 and a sliding contact 42, diodes 44 and 46, a spark igniter 48 and an igniter transformer 50, a step-down voltage transformer 52 having a primary winding 54 and a secondary winding 56, and a pair of power supply leads 58 and 60 for connection to a suitable AC power source.

The oil burner 10 includes the usual blower and fuel pump which when driven by motor 12 supply atomized oil and combustion air to the burner nozzle where it is ignited by spark at electrodes 48. The motor 12 is energized through a circuit traced from power supply lead 60 through a lead 64, motor relay contacts 22, a lead 66,

3,174,528 Patented Mar. 23, 1965 a lead 68, and a lead 70 to power supply lead 58. The igniter transformer 50 is connected in parallel with motor 12 across power supply leads 58 and 68 by leads 72, relay contacts 24, and leads 74 and 76. The motor 12 and igniter are, therefore, energized simultaneously. The only reason for employing the contacts 24 is to reduce current load on the contacts 22.

The motor relay winding 16 is energized initially upon closing of the thermostat through a circuit traced as follows: from the B side of transformer secondary 56 through a lead 78, safety switch 26, a lead 80, diode 46, a lead 82, thermostat 14, a lead 84, a lead 85, the winding 16, a lead 86, a lead 88, resistance heater 32, a lead 90, a lead 94, resistance heater 28, scavenger switch 30, a lead 96, and a lead 98 to the A side of secondary winding 56.

Energization of motor relay winding 16 effects the simultaneous opening of relay contacts 18 and the closing of relay contacts 20, 22, and 24. The closing of contacts 20 completes a low impedance shunting branch in parallel with the safety switch resistance heater 28 which is effective when silicon controlled rectifier 36 is conducting. This parallel branch extends from the junction point 95 of leads and 24 through a lead 100, the silicon controlled rectifier 36, a lead 102, a lead 104, contacts 20, and the lead 98 to the side A of transformer secondary 56.

The silicon controlled rectifier 36 is a four layer PNPN semiconductor device having its anode side Y connected to side B of transformer secondary 56 through leads 100, 90, resistor 32, leads 88, 86, winding 16, leads 85, 84, thermostat 14, lead 82, diode 46, lead 80, switch 26, and leads 78; and having its cathode side X connected to the A side of secondary winding 56 through leads 102, 104, contacts 20, and lead 98. The rectifier 36 is non-conductive at zero bias and includes a control element 36a which when a predetermined plus signal is applied thereto effects conduction through the rectifier.

The light sensitive element 34 is of the semiconductor type which in the absence of burner flame has such high resistance to the flow of electrical current as to block sufficient current flow therethrough which would apply a firing signal to the rectifier control element 36a, but becomes adequately conductive to do so when exposed to the light of burner flame. The light sensitive element 34 is preferably mounted within the burner casing at the rear end of the blast tube. One side of light sensitive element 34 is connected to the B side of transformer secondary 56 through a lead 166, leads 84, thermostat 14, lead 82, diode 46, lead 80, switch 26, and lead 78, so that when side B of secondary 56 is positive and light sensitive element 34 sees burner flame and is conductive, a positive signal is applied to rectifier control element 36a. The application of plus voltage to control element 36a effects conduction through rectifier 36 and the safety switch heater 28 is thereby paralleled by the described low impedance branch extending through switch contacts 20 and is, as a result, rendered inoperative to cause the opening of safety switch 26.

In order that the firing of rectifier 36 may be made to correspond to an optimum light intensity impinging element 34, which is safely above any anticipated ambient light in a particular installation and is yet well within that range of intensity resulting from burner flame, means in the form of the resistor 40 and the sliding contact 42 are provided to vary the effective signal applied to control element 36a. As sliding contact 42 connected to the control element 36a is moved upward on resistor 40, a stronger signal is applied to control element 36a for a given light intensity impinging element 34. It will be noted that irrespective of the position of sliding con tact 42 the series resistance of 40 with respect to the element 34 and its connections to the secondary 56 remain unchanged, and the resistor 40 thereby also serves the purpose of a fiXed current limiter protecting element 34 against excessive current flow.

During that half cycle of the alternating power supply in which the A side of secondary winding 56 is positive, current flow through the circuit is blocked by diode 46, thereby preventing current flow through safety switch heater 28 during this half cycle. Without diode 46 the heater 28 would be heated sufiiciently to cause opening of safety switch 26 even though it is shunted through the silicon controlled rectifier 36 during the half cycle it is conducting. The diode 44 which is connected across the ends of motor relay winding 16 in a manner opposite to that of diode 46 provides a path for sustaining current flow through coil 16 under counter during the non-conductive half cycle, thereby reducing the tendency of the relay to chatter.

The safety switch 26 is normally closed, but when its bimetal blade is heated for a predetermined period of time by the adjacent resistance heater 28, it warps open and locks in an open position, due to latch 29, so as to require manual resetting, This type of safety switch is commonly used and its construction and operation are well understood in the art.

The scavenger switch 39 is also normally closed and has a bimetal blade which, when heated for a sufficient period of time by adjacent heater 32, opens but does not lock open. The scavenger switch closes, therefore, after a predetermined period during which heater 32 is not energized and thereby provides a predetermined delay, the purpose of which is described hereinafter.

In order that the system may be rendered inoperative in event that either the light sensitive element or the silicon controlled rectifier 36 become defectively conductive while the space thermostat is open, a circuit branch extending from the junction 108 to lead 80 through normally closed relay contacts 18, and including leads 110 and 112, is provided. This branch connects the safety switch heater 28 directly across the transformer secondary through the silicon controlled rectifier 36 and the normally closed relay contacts 18, so that if the rectifier 36 becomes conductive for any reason during inoperation of the burner, that is; when thermostat 14 is open or when relay winding 16 is not energized, the safety switch heater 28 will be energized and safety switch 26 will be caused to open and lock open in a relatively hort time.

If light sensitive element 34 becomes sufiiciently conductive for any reason so as to apply a firing signal to rectifier 36 during any time the thermostat is open or when relay winding 16 is de-energized, such signal will be applied to the control element 36a from side A of secondary 56 when it is plus, through lead 96, switch 30, safety switch heater 28, lead 94, lead 90, resistor 32, lead 88, diode 44, lead 106, light sensitive element 34, resistor 40, and sliding contact 42. This application of a firing signal due to faulty conductance through light sensitive element 34 will also result in conduction through rectifier 36 and safety switch heater 28 and will therefore cause the prompt opening of safety switch 26.

Operation of Fig. 1

During normal operation the closing of thermostat 14 upon call for burner operation completes the described circuit for energization of motor relay 16 which may be traced as follows: from the B side of transformer secondary 56 through lead 78, safety switch 26, lead 88, diode 46, lead 82, thermostat 14, lead 84, lead 85, motor relay winding 16, lead 86, lead 88, resistance heater 32, lead 90, lead 94, resistance heater 28, scavenger switch 30, lead 96, and lead 98 to the A side of secondary 56. Completion of this circuit at the space thermostat effects energization of motor relay winding 16 which causes relay contacts 18 to open and contacts 20, 22, and 24 to close, thereby completing the described energizing circuits for burner motor 12 and igniter 50 and completing the shunting circuit branch extending from junction through lead 100, rectifier 36, lead 102, lead 104, contacts 20, and lead 98 to the A side of secondary 56. The rectifier 36 is, however, normally not conductive at this time so that under these conditions the shunting circuit branch is inoperative, and safety switch heater 28 is connected in series with scavenger switch heater 32 and relay winding 16 across the secondary winding 56, as just described. Current flows in one direction only due to diode 46, and the motor relay winding 16 is energized by intermittent unidirectional current flow except as modified by the provision of diode 44.

When combustion at the burner occurs under conditions of normal operation, light sensitive element 34 becomes sufiiciently conductive to fire silicon rectifier 36 and the safety switch heater 28 is shunted to inoperativeness by the circuit branch extending from junction 95 through rectifier 36 and relay contacts 20, so that the safety switch 26 remains closed. This is so because under normal conditions when the thermostat is closed and relay 16 is energized current can only flow through heater 28 in the direction indicated by diode 46. The scavenging switch heater 32, however, is not shunted and remains energized and after a predetermined period effects the opening of scavenger switch 30. The opening of scavenger switch 30 breaks the safety switch heater circuit and the continued heating of scavenging switch heater 32 maintains the scavenger switch 30 in open position thereafter during normal operation. Under these conditions the burner will now operate normally until the thermostat 14 is satisfied and opens.

If at any time prior to the closing of thermostat 14 the silicon controlled rectifier 36 becomes conductive due to faulty conductance through light sensitive element 34, or for any reason, the safety switch heater will be energized through the circuit which may be traced as follows: from the A side of secondary 56, through lead 98, lead 96, scavenger switch 30, safety switch heater 28, lead 94, lead 100, silicon controlled rectifier 36, lead 182, lead 110, normally closed contacts 18, lead 112, lead 80, safety switch 26, and lead 78 to the B side of transformer secondary 56. This effects prompt opening of the safety switch 26, thereby preventing operation of the burner upon subsequent closure of the space thermostat.

If after a normal start the fuel issuing from the burner fails to ignite, the safety switch will open and lock open after a predetermined trial period. If during normal operation of the burner the combustion flame fails for any reason, the resistance of light sensitive element will again become sufficiently high to cut off the signal to control element 36a of the rectifier so that during the succeeding half cycle of the AC. power supply flow through the rectifier will cease. Under these conditions, the scavenging switch 38 being open, operation of the burner motor will be cut off and will remain so for a predetermined scavenging period determined by the time required for the bimetal blade of scavenging switch 30 to cool and close the switch. Upon reclosing of the scavenging switch a trial period will again be initiated as in normal starting. In event the power supply fails momentarily during normal operation a restart can not occur until the scavenging switch 30 closes.

In the form of the invention shown in FIG. 2 of the drawing, operation of the ignition device is cut off after successful combustion is established, the arrangement and operation of the system being otherwise similar to the form shown in FIG. 1, and like numerals are employed to designate like parts.

Referring to FIG. 2 an igniter relay having a winding 114 and normally open contacts 116 is provided. One side of winding 114 is connected to the A side of transformer secondary 56 through leads 118, 120, the scavenging switch heater 30, and leads 96 and 98. The other side of relay winding 114 is connected to the B side of secondary 56 through leads 122, 124, a diode 126, a lead 128, thermostat 14, lead 80, safety switch 26, and lead 78. The primary winding of igniter 50 is connected across the power supply leads 58 and 60 through the relay contacts 116 by the leads 130, 132, 134, and 70. A diode 136 is connected in parallel with relay winding 114 to utilize the current flow resulting from counter during that cycle of the cycle when diode 126 is blocking, thereby to eliminate relay chatter.

Operation of Fig. 2

Under normal operation when thermostat 14 closes energization of igniter relay winding 144 is effected through the circuit described in the preceding paragraph. The energization of winding 114 effects the closing of relay contacts 116, which completes the energizing circuit across the power supply leads for the igniter transformer. and the igniter is rendered operative. When in normal operation the scavenging switch 30 opens, the circuit for relay winding 114 is broken, causing relay contacts 116 to open, and the igniter is rendered inoperative. It will be seen that when starting operation of the system, the scavenging switch heater 32 is in series with safety switch heater 28 due to diode 46, but when in normal operation rectifier 36 becomes conductive, it is connected directly to side A of secondary 56 through rectifier 36 and relay contacts 20 so that its circuit impedance is considerably reduced, and as a result, it heats switch 30 at a faster rate.

In the event combustion fails to occur, conduction through rectifier 36 will not occur and therefore igniter operation is maintained until the system is shut down by the opening of safety switch 26, the time required for heater 32 to open scavenger switch 30 when heater 32 is in series with safety switch heater 28 being somewhat greater than the time required for heater 28 to open the safety switch under these conditions. Under those conditions in which combustion fails to occur, the igniter therefore remains operative up to the time the safety switch opens.

The purpose of diode 126 in the igniter relay winding circuit is to block the flow of current through igniter relay winding 114 after scavenger switch 30 opens. Without the blocking diode 126 current would flow during one half of the cycle from the B side of secondary 56 through safety switch 26, thermostat 14, the relay winding 114, safety switch heater 28, the silicon controlled rectifier 36, and contacts 20 to the A side of secondary 56, so that the scavenger switch 30 would be ineffective to control operation of the igniter and the safety switch would be operated in every instance.

It will be seen from the foregoing that I have provided a particularly simple and economical burner control system which is instantaneously responsive to the appearance or disappearance of burner flame and in which signal amplifying means and relay means usually employed in conjunction with instantaneously responsive flame detectors have been avoided.

I claim:

1. In an electrical circuit for controlling the operation of a burner including in series connection across an alternating power source a relay winding, a normally closed safety switch and a resistance heater which when sufiiciently energized for a predetermined time effects the opening of said switch, and a first normally conductive rectifier, a circuit branch paralleling said resistance heater, 2. second normally nonconductive silicon controlled rectifier in said circuit branch which when conductive passes current through said circuit branch in the same direction as said first rectifier passes current through the main circuit, said silicon controlled rectifier including a control element which when a predetermined plus signal is applied thereto reduces the impedance of said controlled rectifier to the point wherein the energization of said parallel resistance heater is lowered to a point wherein it is rendered inoperative to effect the opening of said switch, circuit connections including a light sensitive element connecting said control element to said circuit thereby to apply a plus signal thereto during that half-cycle when said normally conductive rectifier is passing current, said light sensitive element being shielded from ambient light and being normally nonconductive but being arranged to see flame at a burner and becoming sufiiciently conductive in the presence of burner flame to permit the application of said predetermined plus signal to said con trol element.

2. A circuit as set forth in claim 1 in which said circuit connections connecting said rectifier control element to said circuit further include a manually variable resistor in series with said light sensitive element whereby the intensity of light required to permit the application of the predetermined plus signal to said control element may be preselected.

3. A circuit as seat forth in claim 1 in which said circuit connections connecting said rectifier control element to said circuit comprise a circuit branch which connects the cathode side of said silicon controlled rectifier with said circuit and includes in series relationship a resistor and said light sensitive element, a contactor manually slidable on said resistor and circuit connections connecting said slidable contactor and said control element, whereby the application to the control element of that portion of the available signal due to conduction through said light sensitive element may be selectively varied and whereby said resistor acts in its entirety at all times as a current limiting protector for said light sensitive element.

4. In a burner control system, an alternating current power source, a space thermostat, a relay which when energized causes fuel to be supplied to a burner, said relay including a winding and normally open contacts which close and normally closed contacts which open when said winding is energized, a normally conductive rectifier, a safety switch including a safety warp switch and a resistance heater which when energized for a predetermined period causes the safety warp switch to open and lock open, a normally nonconductive silicon controlled rectifier having a control element which when a plus signal is applied thereto renders the controlled rectifier conductive, and a normally nonconductive light sensitive element which i rendered conductive by the light of burner flame, a first circuit connecting said safety warp switch, said normally conductive rectifier, said thermostat, said relay winding, and said resistance heater in series across said power source with said safety wan-p switoh arranged first and said resistance heater last in said circuit with respect to the direction of current flow, a branch of said circuit including said normally nonconductive controlled rectifier connecting said normally open relay contacts in parallel with said resistance heater and arranged to pass current in the same direction as said normally conductive rectifier, whereby said resistance heater is rendered inoperative by a low impedance shunt when said relay is energized and said controlled rectifier i conducting, a second circuit including said silicon controlled rectifier connecting said resistance heater, said normally closed relay contacts, and said safety warp switch across said power source, whereby both circuits are broken by said safety switch if current passes said controlled rectifier when said relay is not energized, and circuit connections including said light sensitive element connecting said rectifier control element to said circuit at a point wherein a plus signal will be applied thereto from one side of said power source when said space thermostat is closed and said normally conductive rectifier is passing current and from the other side of said power source when said thermostat is open.

5. A system as set forth in claim 4 in which said normally conducting rectifier is a solid state diode.

6. A system as set forth in claim 4 in which said normally conducting rectifier is a solid state diode and in which a second solid state diode is connected across said relay winding in a direction opposing said first diode.

7. A system as set forth in claim 4 which further includes a scavenging switch comprising a resistance heater and a scavenger warp switch which when heated by said heater for a predetermined period opens and subsequently closes in a predetermined time when said heater is deenergized, said scavenger warp switch and its resistance heater being included in series with the recited components of said first circuit and said scavenger warp switch being arranged adjacent said safety switch heater and in that portion of said first circuit which is paralleled by said branch circuit which includes said controlled rectifier and said normally open relay contacts.

8. A system as set forth in claim 4 which further includes a scavenging switch comprising a resistance heater and a scavenger warp switch included in series connection in said first circuit in which said safety warp switch, said space thermostat, said normally conductive rectifier, said relay winding, said scavenger switch heater, said safety switch heater, and said scavenger warp switch are arranged in the recited succession in the direction of flow determined by said normally conductive rectifier, in which both said safety switch heater and said scavenger warp switch are paralleled by said branch including said controlled rectifier and said normally open relay contacts, which further includes an ignition relay including a winding which when energized effects operation of an igniter, and a circuit for said relay winding extending from a point of connection with said first circuit between said safety switch heater and said scavenger warp switch to a point of connection with said first circuit between said space thermostat and said normally conductive rectifier, and including in series connection said relay winding and a second normally conductive rectifier arranged to pass current in a direction opposite to that in which current flows through said first normally conductive rectifier, whereby said igniter relay winding is in series with said scavenger warp switch and said space thermostat, and whereby said second normally conductive rectifier prevents current fiow through said safety switch heater via said ignition relay winding when said cont-rolled rectifier is conducting and said scavenger warp switch is open.

9. In a burner control system, an alternating power source, a main relay which when energized causes fuel to he supplied to a burner, said relay including a winding, normally open contacts which close and normally closed contacts which open when said winding is energized, a safety switch including a normally closed safety warp switch and a resistance heater which when energized for a predetermined time causes said safety warp switch to open and lock open, a space thermostat, a first normally conductive rectifier, a scavenging switch including a normally closed scavenger warp switch which when heated for a predetermined time open and again recloses in a predetermined time when not being heated, and a resistance heater for heating said scavenger warp switch, a normally noncondctive light sensitive element which becomes conductive when burner flame exists, a normally nonconductive silicon controlled rectifier including a control element which when a plus signal is applied thereto becomes conductive, an ignition relay including a winding which when energized effects operation of an ignition device, and a second normally conductive rectifier, a main circuit connecting said safety warp switch, said thermostat, said first normally conductive rectifier, said main relay winding, said scavenger switch heater, said safety switch heater, and said scavenger warp switch in series across said power source in the order recited, a branch circuit paralleling said safety switch heater and said scavenger warp switch and including in series arrangement said silicon controlled rectifier and said normally open relay contacts, said silicon controlled rectifier being arranged to pass current when conducting in the same direction as said normally conductive rectifier, circuit connections with said main circuit including in series arrangement said silicon controlled rectifier and said normally closed relay contacts paralleling said scavenger switch heater, said main relay winding, said first normally conductive rectifier, and said space thermostat, and connecting said scavenger warp switch, said safety switch theater, and said safety warp switch in series arrangement across said power source, circuit connections including said light sensitive element and a current limiting resisto connecting the cathode side of said first normally conductive rectifier with the cathode side of said controlled rectifier, a contactor slidabie on said limiting resistor and a lead connecting said contactor with said rectifier control element, circuit connections with said main circuit extending from a point between said scavenger warp switch and said safety switch heater to a point between said first normally conductive rectifier and said space thermostat and including in series arrangement said ignition relay winding and said second normally conductive rectifier, and said second normally conductive rectifier being arranged to pass cur-rent in a direction opposite to that of said first rectifier.

10. A system as set forth in claim 9 in which said first and second rectifiers are solid state diodes, and in which said light sensitive element is a solid state photoconductive device.

11. A system as set forth in claim 9 in which said first and second normally conductive rectifiers are solid state diodes, in which third and fourth solid state diodes are provided and respectively connected across the ends of said main and ignition relay windings and respectively arranged oppositely to said first and second diodes.

12. A burner control circuit connecting in series relationship across an alternating power source a safety switch including a safety switch resistance heater, a space thermostat, a solid state diode, and the winding of a burner operating relay which when energized reverses the operative positions of normally open and normally closed relay contacts, first circuit connections paralleling said safety switch heater and including in series relationship said normally open relay contacts and a normally nonconductive silicon controlled rectifier having means responsive to the light of burner flame to render it conductive, and second circuit connections paralleling said thermostat, said diode, and said relay winding and including in series said safety switch heater, said silicon controlled rectifier, and said normally closed relay contacts.

13. A burner control circuit as set forth in claim 12 which further includes in series arrangement a scavenging switch comprising a scavenger warp switch and a scavenger resistance heater and in which said scavenger warp switch as well as said safety switch heater is paralleled by said first circuit connections.

References Cited by the Examiner UNITED STATES PATENTS 3,079,982 3/63 Staring 158-28 JAMES W. WESTHAVER, Primary Examiner. 

12. A BURNER CONTROL CIRCUIT CONNECTING IN SERIES RELATIONSHIP ACROSS AN ALTERNATING POWER SOURCE A SAFETY SWITCH INCLUDING A SAFETY SWITCH RESISTANCE HEATER, A SPACE THERMOSTAT, A SOLID STATE DIODE, AND THE WINDING OF A BURNER OPERATING RELAY WHICH WHEN ENERGIZING REVERSES THE OPERATIVE POSITIONS OF NORMALLY OPEN AND NORMALLY CLOSED RELAY CONSTACTS, FIRST CIRCUIT CONNECTIONS PARALLELING SAID SAFETY SWITCH HEATER AND INCLUDING A SERIES RELATIONSHIP SAID NORMALLY OPEN RELAY CONTACTS AND A NORMALLY NONCONDUCTIVE SILICON CONTROLLED RECTIFIER HAVING MEANS RESPONSIVE TO THE LIGHT OF BURNER FLAME TO RENDER IN CONDUCTIVE, AND SECOND CIRCUIT CONNECTIONS PARALLELING SAID THERMOSTAT, SAID DIODE, AND SAID RELAY WINDING AND INCLUDING IN SERIES AND SAFETY SWITCH HEATER, SAID SILICON CONTROLLED RETIFIER, AND SAID NORMALLY CLOSED RELAY CONTACTS. 